No you can not use express lane with any vehicle towing. matter fact in California as you know right two lanes only and 55 MPH limits on any vehicle with towing. one time I asked California Highway Patrol about it, because I have very small 4 ft x 8 ft trailer , light weight empty 200 lbs. Highway patrol man told me , the law is enforced, and both 55 MPH and right two lane only for towing that including my tiny trailer. yes, highway 91 is very crowded , it start to get crowded around 5:00 AM all the way to 9:00 PM Orange County is same.